Running my MacBook pro off one of my DeWalt power tool batteries. There are USB-C adapters for most major tool battery brands out there, many of which (like this one) will both power devices and charge the tool battery from a standard USB-C power plug. YMMV in terms of quality/safety (this is the official dewalt adapter which works great).

Great for power redundancy, etc. A no brainer if you already have the batteries for tools.

@ethanschoonover interesting. I've seen the ones that go over the bigger law tool batteries like Greenworks. But those convert to AC greatly reducing run time (and haven't seen one with USB-C either)